Mo. Rev. Stat. § 416.450
In any case in which a complaint is made in writing to the director by a person claiming to be injured because milk products are being offered for sale or sold in violation of the provisions of sections 416.410 to 416.560, or in which such violations are apparent to the director, the director shall forthwith cause an investigation to be made of the complaint, and if, in the judgment of the director, the investigation reveals that there is probable cause for the complaint, the director shall call upon the attorney general or the prosecuting attorney of any county in which a violation of the provisions of sections 416.410 to 416.560 occurs to institute an injunction suit in a court of competent jurisdiction of the county in which the alleged violations took place to restrain the violations of sections 416.410 to 416.560 as may be revealed by the investigation; and it is the duty of the attorney general or prosecuting attorney to institute and prosecute the injunction suits.
§ 416.450, RSMo